The present invention relates to a connector contact material capable of being inserted with a small insertion force at the time of the connection of a connector, in particular to a connector contact material suitable for multipole terminals of an automobile.
In recent years, as the electrification of an automobile advances, the number of the poles of a multipole connector formed by assembling terminals, namely the number of terminals, has been increasing. A force required for the connection of a connector is roughly estimated by multiplying the insertion force per terminal by the number of wires (heretofore, generally 10 to 20 poles). Hence, when the insertion force per terminal is great, the force required for the connection of a multipole connector considerably increases in proportion to the number of the wires in a wire harness.
In particular, the recent remarkable advancement and development of car electronics cause the number of electronic devices and CPU's mounted on an automobile to increase by leaps and bounds, the number of the wires in a wire harness also increases accordingly, and thus the multipolarization (30 to 40 poles) of a connector has been strongly demanded.
When the number of poles increases as stated above, the force required for the connection of a connector also increases in proportion to the number of wires, the insertion force to fit the connector increases, and the connector becomes increasingly unable to be connected without an auxiliary tool such as a bolt and a lever. In this light, fit-contact-type terminals capable of weakening the insertion force of the terminals and moreover maintaining stable low contact resistance are desired.
As a material for connector contacts, a substance produced by plating a substrate of copper or copper alloy with tin has been used. Tin plating is inexpensive and has good solderability. Further, a tin-plating layer is soft and adheres to a fresh metallic surface at the time of fitting and therefore a good electrical contact can be obtained. However, a tin-plated connector contact material requires a great insertion force and hence is hardly applicable to an aforementioned multipole connector. Furthermore, in the case of frequent insertion and extraction, a tin-plated connector contact material wears markedly, the contact resistance rises due to the exposure and oxidation of the base material, and, in order to inhibit the drawbacks, it is necessary to increase the thickness of the tin-plating layer. In addition, with tin plating, whisker may sometimes occur at plating.
With the intent of solving the problems, methods for lowering contact resistance by applying surface treatment to a connector contact material for multipoles are proposed.
For example, JP-A No. 223290/1998 discloses a technology of lowering contact resistance at a joint and improving wear resistance by connecting a contact member the wear resistance of which is enhanced by hard nickel plating to another contact member to which a composite plating layer formed by the eutectoid of nickel or nickel alloy and fluoric resin particles is applied.
Further, JP No. 2916001 discloses a technology of forming a low-friction conductive layer capable of weakening an insertion force required for connecting a terminal to another terminal while securing the conductivity between electrical contact parts by mixing a superfine conductive metal with a low friction resin material and firmly fixing the mixture to the parts corresponding to the electrical contact parts.
Furthermore, JP-A No. 15743/2000 discloses a means of applying an organic compound containing a thiol group (-SH) as a substantially monomolecular film to a plated material used for a contact of a connector and thereto applying a film of macromolecular aggregate having fluidity as a lubricant layer. It says that, thereby, high resistance to corrosive environment, the stability of contact resistance and lubricity at the joint of a connector can be secured, and therefore it is possible to improve wear resistance even in the case of the frequent fitting of a connector and mitigate the force for the insertion and extraction of the connector.
Yet further, JP-A No. 302866/1998 discloses a technology that makes it possible to weaken an insertion force and secure sufficient corrosion resistance by coating a fit-contact-type terminal to which tin plating 0.1 to 0.3 μm in thickness is applied with a rust preventing lubricant containing a chelating agent and wax.
Yet further, JP-A No. 16623/1999 discloses a technology capable of weakening the insertion force of a terminal by applying coating of carbon in the form of diamond to the slide part of at least either a male component or a female component of a fit-contact-type terminal to which tin plating is applied.
Yet further, JP-A No. 60974/2002 discloses a technology that does not cause the discoloration of the appearance after degradation, improves solderability, and secures excellent slide performance by applying benzotriazole or a derivative thereof so that the thickness thereof, measured as C, is 0.003 to 0.01 μm to the surface of a connector contact material to which copper containing tin plating is applied.
In addition, JP-A No. 212582/2002 discloses a technology that makes it possible to decrease a friction coefficient at the time of the attachment and detachment of an electronic part such as a connector and also lower contact resistance by: applying a coating film of a water-soluble metal surface lubricant produced by emulsifying paraffin, liquid paraffin, or paraffinic carbon hydride of Vaseline or squalene into water with a surfactant; and thereafter drying the coating film.
However, the prior art described in the above documents cannot sufficiently exhibit the effect of weakening an insertion force itself or the effect of weakening an insertion force while maintaining the properties and insertion operability as a connector.
For example, with the technology disclosed in JP-A No. 223290/1998, the effect of weakening an insertion force itself is insufficient.
In the case of JP No. 2916001, a good friction reduction effect can be obtained by firmly fixing a resin material such as Teflon (a registered trademark) to a coating film about 2 to 4 μm in thickness. However, the direct contact between terminals is hindered and, even when conductive metallic fine powder is mixed into the resin layer, the contact between the particles of the metallic powder is not assured, and therefore the conductivity between the terminals is still insufficient. Incidentally, JP No. 2916001 exemplifies the decrease of an insertion force but does not show data related to the conductivity between electric contact parts.
In the technology disclosed in JP-A No. 15743/2000, when it is attempted to secure sufficient lubricity, it is necessary to apply “a film of macromolecular aggregate having fluidity” in a considerable amount. The examples of the coating of poly-α-olefinic oil about 400 μm in thickness, diester oil about 200 μm in thickness and polyphenylether about 100 μm in thickness are described in the embodiments. However, when oil is applied in the thickness of several tens to several hundreds of microns, the flow of the oil and greasiness cannot be avoided on the material surface and the examples are not practically applicable. In addition, when a plated material subjected to such treatment is stacked in layers, sticking (blocking) between the layers caused by the surface tension of the oil occurs and operability is also hindered.
In the case of JP-A No. 302866/1998, long term stability is required for a rust preventing lubricant applied to terminals. However, an ordinary chelating agent and wax are not always excellent in the long term stability.
Though carbon in the form of diamond disclosed in JP-A No. 16623/1999 has an excellent property as a slide member, it is electrically insulative and thus the application of the coating to a conductive part is inappropriate from the viewpoint of lowering contact resistance. The partial application of coating to the surface of a terminal is cumbersome and thus not appropriate for mass production.
With the technology disclosed in JP-A No. 60974/2002, the effect of the oiliness of benzotriazole or a derivative thereof is generally small and therefore a sufficient slide performance cannot be obtained.
In the case of JP-A No. 212582/2002, long term stability is required for a rust preventing lubricant applied to terminals. However, generally speaking, paraffinic carbon hydride is not always excellent in the long term stability. In addition, a water-soluble lubricant has smaller effect in reducing friction than a water-insoluble lubricant.